Amino-containing silane compounds are known useful as surface treating agents which are applied to substrates to render their surfaces hydrophilic and as textile treating agents which are applied to fibers and fabrics to impart hydrophilic properties. Exemplary compounds include aminopropyltrimethoxysilane, aminopropylmethyldimethoxysilane, aminoethylaminopropyltrimethoxysilane, and aminoethylaminopropylmethyldimethoxysilane. While these amino-containing silane compounds can impart hydrophilic properties, they are less effective for imparting antifouling and antifungal properties to the treated surface.
Also known are those compounds capable of imparting not only hydrophilic, but also antifouling and antifungal properties to the treated surface. For example, Patent Document 1 discloses silane compounds having a tetraalkylammonium group such as 3-(trimethoxysilyl)propyloctadecyldimethylammonium chloride. Patent Documents 1 and 2 disclose silane compounds containing a sulfobetaine group and silane compounds containing quaternary ammonium and carboxyl groups.
However, these compounds are still unsatisfactory. Although the tetraalkylammonium-containing silane compounds described in Patent Document 1 can impart antifungal properties, they fail to impart satisfactory antifouling properties because the treated surfaces of substrates or fabrics are electrostatically charged positive by the tetraalkylammonium group, allowing dust and debris to deposit on the surface owing to electrostatic adsorption. Since the sulfobetaine-containing silane compounds described in Patent Documents 2 and 3 and the silane compounds containing tetraalkylammonium and carboxyl groups described in Patent Document 3 form a zwitter-ion in the molecule, the treated surfaces of substrates or fabrics are less electrostatically charged than the treatment with the tetraalkylammonium-containing silane compounds. The sulfobetaine-containing silane compounds have a bias toward the negative charge side due to the sulfonic acid group which is a strong acid, and the silane compounds containing tetraalkylammonium and carboxyl groups have a bias toward the positive charge side due to the tetraalkylammonium group. Because of such a bias from electrical neutrality, no satisfactory antifouling properties are available.